Certain collimated beams such as charged ion beams and electron beams can be used for vaporizing, cutting, welding, and/or melting of metals, as well as for micro fabrication, sputtering, etching, and other useful industrial processes. Effective collimated beam generation typically requires a high vacuum of approximately 10−3 to approximately 10−7 torr, depending on the particular design of the beam generating device. That is, in order to produce or generate a collimated charged particle beam, electron and ion beam generators or sources often require moderate-to-high vacuum conditions, and thus require substantial evacuation of a chamber in which the beam generating device or source is located.
Once generated, the beam exits the vacuum chamber through a hole, aperture, or orifice before propagating through the connected work chamber to a surface of a work piece. The orifice required for passage of the beam may be as large as several millimeters in diameter, a substantial opening which can represent a formidable vacuum leak in the vacuum chamber used for generating the beam. The entire connected working chamber is therefore usually evacuated to the same pressure level as the vacuum chamber.
The need to pump or evacuate the entire working volume of a large ion beam or electron beam system to such a high vacuum as noted above can entail considerable time, complexity, and related expense, and can likewise result in limited throughput. Conventional practice involves the use of differential pumping of intermediate chambers, a practice that can permit use of a collimated beam in a working chamber having a moderately higher pressure than that of the vacuum chamber of the source. However, this approach still requires the use of high-capacity pumps to achieve even moderate working chamber pressure levels, and with relatively small orifice diameters. Moreover, if the working chamber pressure is sufficiently high, the pumping requirement can quickly render as impractical such a differential pumping approach. Beam propagation for significant distances at intermediate pressures can also result in scatter, defocusing, and/or beam attenuation, which can collectively limit both the effectiveness and the utility of the collimated beam.